Immigration Minister Chris Bowen is making no apologies for changing his mind about excising the Australian mainland, saying he would rather save lives than be consistent.

On Wednesday morning the government introduced legislation into the lower house that will excise the Australian mainland from the migration zone. If successful, this would mean all asylum seekers arriving in Australia by boat would be processed offshore.

"This bill marks an important further step in giving full effect to the recommendations of the expert panel on asylum seekers," Mr Bowen told Parliament.

"It removes the incentive for asylum seekers to take greater risks with their lives to reach the Australian mainland."

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The opposition has criticised the move as "breathtaking" hypocrisy, given that Mr Bowen - and other senior Labor figures - were stridently opposed to the idea when John Howard tried to excise the mainland in 2006.

Addressing Parliament in August 2006, Mr Bowen said the proposal to excise Australia was "a bad bill with no redeeming features. It is a hypocritical and illogical bill. If it is passed today, it will be a stain on our national character."

Today, Mr Bowen told ABC Radio that he had changed his mind based on evidence.

"I've changed my mind and this is a change in the Labor Party position, that's very clear, based on the evidence, based on trying to save people's lives," he said.

"If I have a choice between saving somebody's life and being entirely consistent with something I said in 2006, well, I'll go for saving the life, thanks very much."

While the Coalition has yet to declare how it will vote - saying it needs to look at the legislation - already, two of the three Liberal MPs who forced Mr Howard's hand on the issue in 2006 have indicated they will vote against the government's plan, even if the Coalition supports Labor.

"This a flagrant breach of the refugee convention and I will not have a bar of it," Liberal moderate Russell Broadbent said.

But Labor's Left faction will toe the government line despite misgivings about the decision.

Senator Doug Cameron admitted he and his colleagues who preferred a more humanitarian approach had been defeated in caucus yesterday.

He wasn't surprised by the decision given it was one of the recommendations in the Houston report.

"That's when the fight was, and that's when the fight was lost," Senator Cameron told reporters in Canberra.

Amnesty International called the government's migration zone decision "nothing short of absurd".

"The idea that you would take the borders of your country out of your migration zone purely to target people who are trying to come here seeking protection is just an extraordinary thing for any country to do, let alone a country like Australia which helped to draft the Refugee Convention," refugee spokesman Graham Thom said.

Dr Thom said that because it was very rare that people journeyed all the way to Australia, excising the mainland would have little impact on asylum seeker safety.

"People have only tried to get to the nearest Australian territory," he said.

Dr Thomson said that all the legislation would do was send another signal to the region that "it's OK to let politics trump human rights obligations".

Former Liberal MP Bruce Baird, who opposed a the Howard government proposal in 2006, said he was "appalled'' by the Labor move.

''We are basically denying our obligations under the UN convention,'' he said.

"To say that Australia is not Australia for the purposes of asylum seekers — to me, it flies in the face of our human rights arrangements, and shame on those who support it."